Method, apparatus and system for estimating channels

ABSTRACT

A method, an apparatus and a system for estimating channels are disclosed. A method for estimating channels includes: receiving downlink signals inclusive of reference signals from two or more Access Points (APs), where the relative frequency shift between reference signals sent by different APs is zero; and performing channel estimation according to the reference signals. Another method for estimating channels includes: receiving downlink signals inclusive of reference signals from two or more APs, where for a first AP and a second AP among the two or more APs, a specific time-frequency lattice in the downlink signals sent by the first AP does not include data signal, and the specific time-frequency lattice corresponds to a time-frequency lattice utilized by the second AP to send a reference signal; and performing channel estimation according to the reference signals. The technical solution disclosed herein eliminates the interference between the reference signal and the data signal, enables the UE to estimate the channel value between the UE and the cooperative APs accurately, and improves the UE performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/106,054, filed on May 12, 2011, which is a continuation ofInternational Application No. PCT/CN2009/074915, filed on Nov. 12, 2009.The International Application claims priority to Chinese PatentApplication No. 200810226468.7, filed on Nov. 12, 2008 Theafore-mentioned patent applications are hereby incorporated by referencein their entireties.

FIELD OF THE INVENTION

The present invention relates to communication technologies, and inparticular, to a method, an apparatus and a system for estimatingchannels.

BACKGROUND OF THE INVENTION

In a radio communication system, Coordinated Multi-Point (CoMP)transmission is a technology for improving overall performance of a celland performance of users at the edge of the cell. Downlink CoMPtransmission is a technology for multiple geographically distributedtransmitters to jointly send data to a User Equipment (UE). In a CoMPsystem, network nodes include an evolved NodeB (eNodeB) and severalAccess Points (APs). An AP is a node that includes at least a radiofrequency transceiver, and one or more antenna units can be configuredon the AP. Multiple APs are geographically distributed and connected tothe eNodeB, and can coordinate to transmit or receive data from the UE.The cooperative APs may be connected with a same eNodeB or differenteNodeBs. In a CoMP system, multiple cooperative cells/APs send a samesignal to the UE jointly, which enhances the power of the UE forreceiving the signal and improves the performance of the UEs at the edgeof the cells/APs. However, to receive signals from multiple cooperativecells/APs effectively, the UE needs to estimate the channel valuebetween the UE and the cooperative cells/APs accurately.

In a Long Term Evolution (LTE) system, a reference signal pattern is putforward. The reference signal pattern includes common reference signalsand dedicated reference signals. The common reference signals alwaysexist, and are bound to a cell identity (ID); and the dedicatedreference signals are bound to a UE ID and a cell ID.

In the conventional art, dedicated pilot frequencies are generally usedto implement CoMP applications. In this way, the CoMP system is wellcompatible with the LTE system, without any extra signaling overhead.However, if the reference signal pattern provided by the LTE system isapplied to the CoMP system, when multiple cooperative cells/APs serve aUE jointly, the reference signal interferes with the data signalreciprocally for every two cooperative cells/APs. Consequently, the UEis unable to estimate the channel value between the UE and thecooperative cells/APs accurately, which affects the performance of theUE seriously.

SUMMARY OF THE INVENTION

The primary technical problem to be solved by the present invention isto provide a method, an apparatus and a system for estimating channelsso that a UE can estimate the channel value between the UE and thecooperative cells/APs accurately when multiple cooperative cells/APsserve the UE jointly.

To solve the above technical problem, according to the first aspect ofthe present invention, a channel estimation method includes thefollowing steps:

receiving downlink signals inclusive of reference signals from two ormore APs, where a relative frequency shift between reference signalssent by different APs is zero; and

performing channel estimation according to the reference signals.

According to the second aspect of the present invention, another channelestimation method includes the following steps:

receiving, by a User Equipment (UE), downlink signals inclusive ofreference signals from two or more Access Points (APs), wherein aspecific time-frequency lattice in the downlink signals sent by a firstAP among the two or more APs does not comprise data signal, and thespecific time-frequency lattice corresponds to a time-frequency latticeutilized by a second AP among the two or more APs to send a referencesignal; and

performing, by the UE, channel estimation according to the referencesignals.

According to the third aspect of the present invention, another channelestimation method includes the following steps:

receiving, by a User Equipment (UE), downlink signals sent by two ormore Access Points (APs), wherein no common reference signal iscomprised in any data channel symbol domain except a preset symboldomain in the downlink signals; and

performing, by the UE, channel estimation according to the downlinksignals.

According to the fourth aspect of the present invention, a channelestimation apparatus includes:

a receiver, configured to receive downlink signals inclusive ofreference signals from two or more Access Points (APs), wherein: arelative frequency shift between reference signals sent by different APsis zero; or, a specific time-frequency lattice in the downlink signalssent by a first AP among the two or more APs does not comprise datasignal, and the specific time-frequency lattice corresponds to atime-frequency lattice utilized by a second AP among the two or more APsto send a reference signal; or, no common reference signal is comprisedin any data channel symbol domain except a preset symbol domain in thedownlink signals; and

an estimating unit, configured to perform channel estimation accordingto the reference signals.

According to the fifth aspect of the present invention, a channelestimation system includes:

a channel estimation apparatus, configured to receive downlink signalsinclusive of reference signals from two or more Access Points (APs) andperform channel estimation according to the reference signals, wherein:a relative frequency shift between reference signals sent by differentAPs is zero; or, a specific time-frequency lattice in the downlinksignals sent by a first AP among the two or more APs does not comprisedata signal, and the specific time-frequency lattice corresponds to atime-frequency lattice utilized by a second AP among the two or more APsto send a reference signal; or, no common reference signal is comprisedin any data channel symbol domain except a preset symbol domain in thedownlink signals.

It can be seen from the above that, in the downlink signals received inthe present invention, the relative frequency shift between referencesignals sent by different APs is zero; or, a specific time-frequencylattice does not include data signal; or, no common reference signal isincluded in any data channel symbol domain except a preset symboldomain. In this way, the interference between the reference signal andthe data signal is eliminated, the UE can estimate the channel valuebetween the UE and the cooperative cells/APs accurately, and the UEperformance is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows reference signals of a first AP in an LTE system accordingto an embodiment of the present invention;

FIG. 1B shows reference signals of a second AP in an LTE systemaccording to an embodiment of the present invention;

FIG. 2 is a flowchart of a channel estimation method provided accordingto a first embodiment of the present invention;

FIG. 3A shows reference signals of a first AP in a channel estimationmethod provided according to a second embodiment of the presentinvention;

FIG. 3B shows reference signals of a second AP in a channel estimationmethod provided according to the second embodiment of the presentinvention;

FIG. 3C shows reference signals of a first AP in a channel estimationmethod provided according to the second embodiment of the presentinvention;

FIG. 3D shows reference signals of a second AP in a channel estimationmethod provided according to the second embodiment of the presentinvention;

FIG. 4 is a flowchart of a channel estimation method provided accordingto a third embodiment of the present invention;

FIG. 5A shows reference signals of a first AP in a channel estimationmethod provided according to a fourth embodiment of the presentinvention;

FIG. 5B shows reference signals of a second AP in a channel estimationmethod provided according to the fourth embodiment of the presentinvention;

FIG. 6 is a flowchart of another channel estimation method providedaccording to a first embodiment of the present invention;

FIG. 7A shows reference signals of a first AP in another channelestimation method provided according to a second embodiment of thepresent invention;

FIG. 7B shows reference signals of a second AP in another channelestimation method provided according to the second embodiment of thepresent invention;

FIG. 8 is a flowchart of another channel estimation method providedaccording to a fourth embodiment of the present invention;

FIG. 9 is a flowchart of another channel estimation method providedaccording to a first embodiment of the present invention; and

FIG. 10 shows a structure of a channel estimation apparatus providedaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following detailed description is given with reference to theaccompanying drawings to provide a thorough understanding of the presentinvention. Evidently, the drawings and the detailed description aremerely representative of particular embodiments of the present inventionrather than all embodiments. All other embodiments, which can be derivedby those skilled in the art from the embodiments given herein withoutany creative effort, shall fall within the scope of the presentinvention.

The technical solution under the present invention is expounded belowwith reference to accompanying drawings and preferred embodiments.

The relation between an AP and a traditional cell is: A cell includesone or more APs. When the reference signals change per cell, a relativeshift exists between reference signals of every two cooperative cells;when the reference signals change per AP, a relative shift existsbetween reference signals of every two cooperative APs. In the followingembodiments, it is assumed that the reference signals change per AP, andthat the processing mode is similar when the reference signals changeper cell.

FIG. 1A and FIG. 1B show reference signals of the first AP and thesecond AP in an LTE system in an embodiment of the present invention,and show a pattern of a subframe in the first AP and the second AP whichserve the same UE. In FIG. 1A and FIG. 1B, a row represents a timedomain, and a column represents a frequency domain. Specifically,different rows represent different Orthogonal Frequency DivisionMultiplexing (OFDM) symbol domains. The figure shows 14 rows in total,which represent 1 ms. Different columns represent different subcarriers.The figure shows 12 columns in total, which represent 12 subcarriers.R0, R1, R2 and R3 represent the common reference signals of ports 0-3respectively; Rd represents a dedicated reference signal; and S1 and S2are data signals. As shown in FIG. 1A and FIG. 1B, for two differentAPs, a relative frequency shift exists between the common referencesignal and the dedicated reference signal.

In the following embodiments, by changing the mode of the referencesignals shown in FIG. 1A and FIG. 1B, the method put forward hereinchanges the sending mechanism of the cooperative APs and the receivingmechanism of the UE, and solves mutual interference between thereference signal and the data signal. A preliminary step performedbefore the steps of the following embodiments is: The eNodeB judgeswhether the UE is in cooperative mode, namely, whether multiplecooperative APs serve one UE; if not, the AP sends reference signalsshown in FIG. 1A and FIG. 1B to the UE; if so, the AP performs the stepsof the following embodiments. Further, if the eNodeB determines that theUE changes from the non-cooperative mode to the cooperative mode,namely, one AP serving a UE changes to multiple cooperative APs servingthe UE, the method in this embodiment further includes: When multiplecooperative APs belong to the same eNodeB, the eNodeB instructs multiplecooperative APs to change the mode of the reference signals, and themultiple cooperative APs instruct the UE to change the mode of thereference signals. When multiple cooperative APs belong to differenteNodeBs, the eNodeBs instruct each other to change the mode of thereference signals, and instruct the multiple cooperative APs to changethe mode of the reference signals. Moreover, the multiple cooperativeAPs instruct the UE to change the mode of the reference signals.

It should be noted that in the embodiments of the present invention, thedownlink signals include control channel symbol domains and data channelsymbol domains. Generally, several initial rows represent controlchannel symbol domains, and the remaining rows are data channel symboldomains. In the subframes shown in FIG. 1A and FIG. 1B, the first tworows represent the control channel symbol domain, and other rows aredata channel symbol domains. While the AP delivers downlink signals, thenumber of rows corresponding to the control channel symbol domains isvariable. That is, in different subframes, the number of rowscorresponding to the control channel symbol domains may differ. A“preset symbol domain” involved in the following embodiments refers tothe symbol domain to be most probably occupied by the control channel.For certain subframes, the number of rows corresponding to the controlchannel symbol domain is less than the number of rows corresponding tothe preset symbol domain. Therefore, the preset symbol domain may alsoinclude data signals.

The first embodiment of a channel estimation method is described below:

FIG. 2 is a flowchart of a channel estimation method provided in thefirst embodiment of the present invention. The method includes thefollowing steps:

Step 101: Receive downlink signals inclusive of reference signals fromtwo or more APs, where a relative frequency shift between referencesignals sent by different APs is zero.

When this embodiment is applied in a CoMP system, the UE receives thedownlink signals sent by two or more cooperative APs. This embodimentchanges the mode of the reference signals shown in FIG. 1A and FIG. 1Bso that no relative frequency shift exists between the reference signalssent by different APs, namely, the relative frequency shift is zero. Thecooperative APs send the reference signals to the UE according to thesending mechanism corresponding to the changed reference signals, andthe UE receives the reference signals according to the receivingmechanism corresponding to the changed reference signals.

Step 102: Perform channel estimation according to the reference signals.

This embodiment is applicable to the scenario where two or morecooperative APs send the same data signal to the UE, and applicable tothe scenario where two or more cooperative APs send different datasignals to the UE.

No relative frequency shift exists between the reference signals sent bydifferent APs. Therefore, the reference signal does not interfere withthe data signal reciprocally, the UE can estimate the channel valuebetween the UE and the cooperative APs accurately, and the UEperformance is improved.

The second embodiment of a channel estimation method is described below:

FIG. 3A and FIG. 3B show reference signals of a first AP and a second APrespectively in a channel estimation method in the second embodiment ofthe present invention. The processing method in this embodiment is thesame as that in the first embodiment above. This embodiment givesdetails about how to change the mode of the reference signals.

Dedicated reference signals are taken as an example here. It is assumedthat any two APs among two or more APs are a first AP and a second AP.The two APs are the cooperative APs that serve the same UE. FIG. 3A andFIG. 3B show the reference signals of the first AP and the second APrespectively. In comparison with FIG. 1B, the frequency shift of thededicated reference signals of the second AP in FIG. 3B has changed. Norelative frequency shift exists between the dedicated reference signalof the first AP and that of the second AP, namely, the relativefrequency shift between the dedicated reference signal of the first APand that of the second AP is zero. In this way, when the cooperative APssend the same downlink signal to the UE to enhance the signal, the UEcan estimate the channel value between the UE and the cooperative APsaccurately according to the dedicated reference signal, and thenestimate the aggregated channel (in other words, perform soft combiningfor the channels).

This embodiment may also change the frequency shift of the commonreference signal of the second AP, and therefore, no frequency shiftexists between the common reference signal of the first AP and that ofthe second AP, and the interference between the common reference signaland the data signal is eliminated. Further, the downlink signals mayinclude no dedicated reference signal, thus eliminating interferencebetween the dedicated reference signal and the data signal.

In this embodiment, the UE can receive the common reference signalaccording to the receiving mechanism corresponding to the changed commonreference signal, or receive the dedicated reference signal according tothe receiving mechanism corresponding to the changed dedicated referencesignal, thus improving the UE performance effectively. Preferably, boththe relative frequency shift of the common reference signal and therelative frequency shift of the dedicated reference signal are changedin the foregoing way. FIG. 3C and FIG. 3D show reference signals of afirst AP and a second AP respectively in a channel estimation method inthe second embodiment of the present invention. This embodimenteliminates the interference between the common reference signal and thedata signal, and the interference between the dedicated reference signaland the data signal. In this way, the UE can estimate the channel valuebetween the UE and the cooperative APs accurately, and improve theperformance of the UE effectively.

That is, this embodiment can receive the downlink signals in which thededicated reference signal has a relative frequency shift but the commonreference signal has no relative frequency shift; or receive thedownlink signals in which the dedicated reference signal has no relativefrequency shift but the common reference signal has a relative frequencyshift; or receive the downlink signals in which the dedicated referencesignal has no relative frequency shift and the common reference signalhas no relative frequency shift.

The third embodiment of a channel estimation method is described below:

The processing method in this embodiment is the same as that in thefirst embodiment above. Specifically, the reference signal is adedicated reference signal; in the same way as obtaining the dedicatedreference signal in the second embodiment above, this embodiment canobtain the dedicated reference signal whose relative frequency shift iszero. Differently, this embodiment uses an interference eliminationmethod to eliminate the interference between the common reference signaland the data signal.

FIG. 4 is a flowchart of a channel estimation method provided in thethird embodiment of the present invention. On the basis of the firstembodiment, step 102 may include the following steps:

Step 1021: Regard data signals in the downlink signals as interferencesignals, and perform channel estimation.

The data signals may be regarded as interference signals to performchannel estimation.

Step 1022: Estimate the data signals according to the result of channelestimation.

Step 1023: Eliminate the data signals in the downlink signals accordingto the result of estimating the data signals, and perform channelestimation. Specifically, subtract estimated data signals from thedownlink signals, eliminate the interference caused by the data signals,and estimate the channel again.

Steps 1021-1023 are an iterative process. To better eliminate the impactcaused by the data signals, the foregoing steps may be repeated.

The fourth embodiment of a channel estimation method is described below:

The processing method in this embodiment is the same as that in thefirst embodiment above. Specifically, the reference signal is adedicated reference signal; in the same way as obtaining the dedicatedreference signal in the second embodiment above, this embodiment canobtain the dedicated reference signal whose relative frequency shift iszero. This embodiment differs in that: No common reference signal isincluded in the data channel symbol domains except the preset symboldomain in the downlink signals, so that the interference between thecommon reference signal and the data signal can be eliminated.

FIG. 5A and FIG. 5B show reference signals of a first AP and a second APrespectively in a channel estimation method in the fourth embodiment ofthe present invention. In FIG. 5A and FIG. 5B, the first two rows arethe symbol domains to be most probably occupied by the control channel,and are preset symbol domains. The symbol domains except the first tworows are data channel symbol domains. The data channel symbol domainscarry no common reference signal, but carry the dedicated referencesignals only. In this way, the interference between the common referencesignal and the data signal is eliminated as much as possible.

Further, to eliminate the interference between the common referencesignal and the data signal in the preset symbol domain, this embodimentcan change the frequency shift of the common reference signal in thepreset symbol domain in the second AP, and therefore, no relativefrequency shift exists between the common reference signal in the presetsymbol domain in the second AP and the common reference signal in thepreset symbol domain in the first AP.

In another embodiment, the interference elimination method in steps1021-1023 are applied to further eliminate the interference between thecommon reference signal in the preset symbol domain and the data signal.

The first embodiment of another channel estimation method is describedbelow:

FIG. 6 is a flowchart of another channel estimation method provided in afirst embodiment of the present invention. The method includes thefollowing steps:

Step 201: Receive downlink signals inclusive of reference signals fromtwo or more APs. Among the two or more APs (one is a first AP, and theother is a second AP), a specific time-frequency lattice in the downlinksignals sent by the first AP does not include data signal, where thespecific time-frequency lattice corresponds to a time-frequency latticeutilized by the second AP to send the reference signal.

When this embodiment is applied to a CoMP system, the UE receives thedownlink signals sent by two or more cooperative APs. For the downlinksignals sent by each AP, if the reference signals shown in FIG. 1A andFIG. 1B are applied, no data signal is sent at specific time-frequencylattices corresponding to the time-frequency lattice of the referencesignal sent by other APs. For example, if the UE receives downlinksignals sent by three APs, for each of the APs, the time-frequencylattice of the reference signal sent by other two APs corresponds to thespecific time-frequency lattice of this AP, and no data signal is sentat the specific time-frequency lattice of this AP. The cooperative APssend the reference signals to the UE according to the changed sendingmechanism corresponding to the reference signals, and the UE receivesthe reference signals according to the receiving mechanism correspondingto the changed reference signals.

Step 202: Perform channel estimation according to the reference signals.

Because no data signal is sent at the specific time-frequency lattice,the reference signal does not interfere with the data signalreciprocally, the UE can estimate the channel value between the UE andthe cooperative APs accurately, and the UE performance is improved.

The second embodiment of another channel estimation method is describedbelow:

FIG. 7A and FIG. 7B show reference signals of a first AP and a second APrespectively in a channel estimation method in the second embodiment ofthe present invention. The processing method in this embodiment is thesame as that in the first embodiment above.

Taking the dedicated reference signal as an example, it is assumed thatany two APs among two or more APs are a first AP and a second AP. Thetwo APs are the cooperative APs that serve the same UE. FIG. 7A and FIG.7B show the reference signals of the first AP and the second APrespectively. In comparison with FIG. 1A, no data signal is sent at thespecific time-frequency lattice (illustrated by the area filled withoblique lines in FIG. 7A) in the downlink signals of the first AP inFIG. 7A. The specific time-frequency lattice in FIG. 7A corresponds tothe time-frequency lattice of the sent reference signal in FIG. 7B. Forexample, the specific time-frequency lattice A in FIG. 7A corresponds tothe time-frequency lattice B in FIG. 7B. If the signal sent attime-frequency lattice B is a reference signal, no data signal is sentat the specific time-frequency lattice A. By analogy, in comparison withFIG. 1B, no data signal is sent at the specific time-frequency lattice(illustrated by the area filled with oblique lines in FIG. 7B) in thedownlink signals of the second AP in FIG. 7B. The specifictime-frequency lattice in FIG. 7B corresponds to the time-frequencylattice of the sent reference signal in FIG. 7A. In this way, when thecooperative APs send the same downlink signal to the UE to enhance thesignal, the dedicated reference signal does not interfere with the datasignal reciprocally, and the UE can estimate the channel value betweenthe UE and the cooperative APs accurately according to the dedicatedreference signal, and then estimate the aggregated channel. Thisembodiment is applicable to the scenario where two or more cooperativeAPs send the same data signal to the UE, and applicable to the scenariowhere two or more cooperative APs send different data signals to the UE.

Similar methods may be applied to eliminate the interference between thecommon reference signal and the data signal. For two or more APs (one isa first AP, and the other is a second AP), no data signal is sent at thespecific time-frequency lattice corresponding to the common referencesignal sent by the second AP in the downlink signals sent by the firstAP. It should be noted that to ensure accuracy of control information,the specific time-frequency lattice sending no data signal may belocated in the data channel symbol domain of the downlink signal. Thatis, the sending mechanism is not changed at the symbol domaincorresponding to the downlink control channel, but is changed at asymbol domain other than the symbol domain corresponding to the downlinkcontrol channel; and no data signal is sent at the specifictime-frequency lattice. This embodiment is applicable to the scenariowhere two or more cooperative APs send the same data signal to the UE,and applicable to the scenario where two or more cooperative APs senddifferent data signals to the UE.

In this embodiment, the UE can receive the common reference signalaccording to the changed sending mechanism corresponding to the commonreference signal, or receive the dedicated reference signal according tothe changed sending mechanism corresponding to the dedicated referencesignal, thus improving the UE performance effectively. Preferably, thesending mechanism of both the common reference signal and the dedicatedreference signal is changed through the foregoing method to eliminatethe interference between the common reference signal and the data signalas well as the interference between the dedicated reference signal andthe data signal. In this way, the UE can estimate the channel valuebetween the UE and the cooperative APs accurately, and improve theperformance of the UE effectively.

That is, this embodiment can receive the downlink signals in which thededicated reference signal has a relative frequency shift but thespecific time-frequency lattice does not include data signal; or receivethe downlink signals in which the common reference signal has a relativefrequency shift but the specific time-frequency lattice does not includedata signal; or receive the downlink signals in which the dedicatedreference signal has a relative frequency shift, the specifictime-frequency lattice of the dedicated reference signal does notinclude data signal, and the common reference signal has a relativefrequency shift but the specific time-frequency lattice of the commonreference signal does not include data signal.

The third embodiment of another channel estimation method is describedbelow:

The processing method in this embodiment is the same as that in thefirst embodiment above. Specifically, the processed reference signalsare dedicated reference signals; the practice of changing the sendingmechanism of the dedicated reference signal in the second embodiment isalso applicable in this embodiment. This embodiment differs in that:This embodiment changes the frequency shift of the common referencesignal sent by either of the APs to achieve a zero relative frequencyshift between the common reference signals sent by different APs andeliminate the interference between the common reference signal and thedata signal. The combination of the two methods eliminates theinterference between the common reference signal and the data signal,and the interference between the dedicated reference signal and the datasignal. In this way, the UE can estimate the channel value between theUE and the cooperative APs accurately, and improve the performance ofthe UE effectively.

Similarly, the processed reference signals may be common referencesignals, and the interference between the dedicated reference signal andthe data signal can be eliminated by changing the frequency shift.

The fourth embodiment of another channel estimation method is describedbelow:

The processing method in this embodiment is the same as that in thefirst embodiment above. Specifically, the reference signals arededicated reference signals; the practice of changing the sendingmechanism of the dedicated reference signal in the second embodiment isalso applicable in this embodiment. Differently, this embodiment uses aninterference elimination method to eliminate the interference betweenthe common reference signal and the data signal.

Similarly, the processed reference signals may be common referencesignals, and the interference between the dedicated reference signal andthe data signal can be eliminated through an interference eliminationmethod.

FIG. 8 is a flowchart of another channel estimation method provided inthe fourth embodiment of the present invention. Step 202 in the firstembodiment above may include steps 2021-2023. Steps 2021-2023 are thesame as steps 1021-1023 in the previous embodiment.

The fifth embodiment of another channel estimation method is describedbelow:

The processing method in this embodiment is the same as that in thefirst embodiment above. Specifically, the reference signals arededicated reference signals; the practice of changing the sendingmechanism of the dedicated reference signal is also applicable in thisembodiment. This embodiment differs in that: No common reference signalis included in the data channel symbol domains except the preset symboldomain in the downlink signals, so that the interference between thecommon reference signal and the data signal can be eliminated. Thecombination of the two methods eliminates the interference between thecommon reference signal and the data signal, and the interferencebetween the dedicated reference signal and the data signal. In this way,the UE can estimate the channel value between the UE and the cooperativeAPs accurately, and improve the performance of the UE effectively.

Further, to eliminate the interference between the common referencesignal and the data signal in the preset symbol domain, this embodimentcan change the frequency shift of the common reference signal in thepreset symbol domain in either of the APs, and therefore, no relativefrequency shift exists between the common reference signal in the presetsymbol domain in one AP and the common reference signal in the presetsymbol domain in the other AP.

In another embodiment, the interference elimination method in steps2021-2023 are applied to further eliminate the interference between thecommon reference signal in the preset symbol domain and the data signal.

The first embodiment of another channel estimation method is describedbelow:

FIG. 9 is a flowchart of another channel estimation method provided in afirst embodiment of the present invention. This embodiment involveswhether the cooperative APs send the common reference signal. The methodincludes the following steps:

Step 301: Receive downlink signals sent by two or more APs, where nocommon reference signal is included in any data channel symbol domainexcept a preset symbol domain in the downlink signals.

When this embodiment is applied in a CoMP system, the UE receivesdownlink signals sent by two or more APs. This embodiment changes themode of the reference signals shown in FIG. 1A and FIG. 1B so that nocommon reference signal is included in any data channel symbol domainexcept the preset symbol domain in the downlink signals. The “presetsymbol domain” refers to the symbol domain to be most probably occupiedby the control channel. The cooperative APs send the reference signalsto the UE according to the changed sending mechanism corresponding tothe reference signals, and the UE receives the reference signalsaccording to the receiving mechanism corresponding to the changedreference signals.

Step 302: Perform channel estimation according to the downlink signals.

Because no common reference signal is included in the data channelsymbol domain, the common reference signal does not interfere with thedata signal reciprocally, the UE can estimate the channel value betweenthe UE and the cooperative APs accurately, and the UE performance isimproved.

The second embodiment of another channel estimation method is describedbelow:

The processing method in this embodiment is the same as the firstembodiment of another channel estimation method except that the presetsymbol domain of the downlink signals does not include common referencesignal, namely, the dedicated reference signal instead of the commonreference signal is sent from the control channel symbol domain and thedata channel symbol domain of the currently scheduled subframe. Further,the common reference signal of the currently scheduled subframe can beestimated according to the common reference signal of the adjacentsubframe not scheduled currently. In this way, the interference betweenthe common reference signal and the data signal in the currentlyscheduled subframe is eliminated, and the interference between thecommon reference signal and the control signal is eliminated.

The third embodiment of another channel estimation method is describedbelow:

The processing method in this embodiment is the same as the firstembodiment of the channel estimation method, and the preset symboldomain of the downlink signals includes a common reference signal. Thedifference is that: No data signal is sent at certain time-frequencylattices of the preset symbol domain. Specifically, for the first AP andthe second AP among the two or more APs, the specific time-frequencylattice of the preset symbol domain in the downlink signals sent by thefirst AP does not include data signal, and the specific time-frequencylattice corresponds to the time-frequency lattice of the commonreference signal sent by the second AP.

Because the preset symbol domain is the symbol domain to be mostprobably occupied by the control channel, for certain subframes, thenumber of rows corresponding to the control channel symbol domain isless than the number of rows corresponding to the preset symbol domain.Therefore, the preset symbol domain may also include data signals. Inthis embodiment, to eliminate the interference between the data signaland the common reference signal in the preset symbol domain, no datasignal is sent at the specific time-frequency lattice of the presetsymbol domain.

All the embodiments above are applied to the UEs in cooperative mode.However, the embodiments of the present invention are applicable to theUEs in non-cooperative mode as well. When the channel estimation methodis applied to both the UEs in cooperative mode and the UEs innon-cooperative mode, the system structure is simplified, and the systemimplementation is simpler. Moreover, in the embodiments of the presentinvention, the dedicated reference signals include, but are not limitedto, the signals of port 5 in the existing LTE system; and may includededicated reference signals added in the future.

In a CoMP system, some UEs communicate with one AP, and some UEscommunicate with multiple APs simultaneously. Therefore, for an AP, thecooperative mode may be combined with the non-cooperative mode.

An embodiment of a channel estimation apparatus is described below:

FIG. 10 shows a structure of a channel estimation apparatus provided inan embodiment of the present invention. The apparatus includes areceiver 11 and an estimating unit 12. The receiver 11 receives downlinksignals inclusive of reference signals from two or more APs. Theestimating unit 12 performs channel estimation according to thereference signals. To eliminate interference between the referencesignal and the data signal, one practice is: The relative frequencyshift between reference signals sent by different APs is zero; anotherpractice is: For two or more APs (one is a first AP, and the other is asecond AP), a specific time-frequency lattice in the downlink signalssent by the first AP does not include data signal, where the specifictime-frequency lattice corresponds to the time-frequency latticeutilized by the second AP to send the reference signal. The two modesabove are applicable to both common reference signals and/or dedicatedreference signals. Another practice is: No common reference signal isincluded in any data channel symbol domain except a preset symbol domainin the downlink signals. This practice eliminates the interferencebetween the reference signal and the data signal, enables the UE toestimate the channel value between the UE and the cooperative APsaccurately, and improves the UE performance.

When the foregoing practice is applied to the dedicated referencesignals but not applied to the common reference signals, the estimatingunit 12 may include a first estimating unit 12A, a second estimatingunit 12B, and a third estimating unit 12C. The first estimating unit 12Aregards the data signals in the downlink signals as interference signalsto perform channel estimation. The second estimating unit 12B estimatesthe data signals according to the result of channel estimation. Thethird estimating unit 12C eliminates the data signals in the downlinksignals according to the result of estimating the data signals, andperforms channel estimation.

It should be noted that several methods are provided herein to eliminatethe interference between the reference signal and the data signal (seethe method embodiments above), and that the channel estimation apparatusdisclosed herein is applicable to any embodiment of the channelestimation method above.

The receiver is specifically configured to receive downlink signalsinclusive of common reference signals from two or more APs, where thedownlink signals include no dedicated reference signals.

Or, the receiver is specifically configured to receive downlink signalsinclusive of dedicated reference signals from two or more APs, where nocommon reference signal is included in any data channel symbol domainexcept a preset symbol domain in the downlink signals.

Or, the receiver is specifically configured to receive downlink signalsinclusive of dedicated reference signals from two or more APs, where: nocommon reference signal is included in any data channel symbol domainexcept a preset symbol domain in the downlink signals, and a relativefrequency shift between the common reference signals included in thepreset symbol domain is zero.

Or, the receiver is specifically configured to receive downlink signalsinclusive of dedicated reference signals from two or more APs, where:the downlink signals further include common reference signals, and therelative frequency shift between the common reference signals sent bydifferent APs is zero.

Or, the receiver is specifically configured to receive downlink signalsinclusive of common reference signals from two or more APs, where thespecific time-frequency lattice is located in the data channel symboldomain of the downlink signals.

Or, the receiver is specifically configured to receive downlink signalsinclusive of reference signals from two or more APs, where: a presetsymbol domain in the downlink signals includes common reference signals,a specific time-frequency lattice in a preset symbol domain in thedownlink signals received from a first AP among the two or more APs doesnot include data signal, and the specific time-frequency latticecorresponds to a time-frequency lattice of a common reference signalsent by a second AP among the two or more APs.

An embodiment of a channel estimation system is described below:

The system includes a channel estimation apparatus, which is configuredto receive downlink signals inclusive of reference signals from two ormore APs and perform channel estimation according to the referencesignals, where: a relative frequency shift between reference signalssent by different APs is zero; or, a specific time-frequency lattice inthe downlink signals sent by a first AP among the two or more APs doesnot include data signal, and the specific time-frequency latticecorresponds to a time-frequency lattice utilized by a second AP amongthe two or more APs to send a reference signal; or, no common referencesignal is included in any data channel symbol domain except a presetsymbol domain in the downlink signals. The system in this embodimenteliminates the interference between the reference signal and the datasignal, enables the UE to estimate the channel value between the UE andthe cooperative APs accurately, and improves the UE performance.

Persons of ordinary skill in the art should understand that all or partof the steps of the method according to the embodiments of the presentinvention may be implemented by a program instructing relevant hardware.The program may be stored in computer readable storage media. When theprogram runs, the steps of the method specified in an embodiment of thepresent invention are performed. The storage media may be any mediacapable of storing program codes, such as a Read Only Memory (ROM), aRandom Access Memory (RAM), a magnetic disk, or a Compact Disk-Read OnlyMemory (CD-ROM).

It is understandable to those skilled in the art that the accompanyingdrawings are only schematic diagrams of the preferred embodiments, andthat the units or processes in the accompanying drawings are notmandatory for implementing the present invention.

It is understandable to those skilled in the art that the units in anapparatus provided in an embodiment of the present invention may bedistributed into the apparatus described herein, or may be located inone or more apparatuses different from the apparatus described herein.The units may be integrated into one unit, or split into multiplesubunits.

The serial number of each embodiment above is given for ease ofdescription only and does not represent the order of preference of theembodiment.

The above descriptions are merely preferred embodiments of the presentinvention, but not intended to limit the scope of the present invention.Any modifications or variations that can be derived by those skilled inthe art shall fall within the scope of the present invention.

1. A channel estimation method, comprising: receiving, by a UserEquipment (UE), downlink signals inclusive of reference signals from afirst Access Points (AP) and a second AP, wherein a specifictime-frequency lattice in the downlink signals sent by the first AP doesnot comprise data signal, the specific time-frequency latticecorresponds to a time-frequency lattice utilized by the second AP tosend a reference signal, and time-frequency lattices utilized by thefirst AP and the second AP to send reference signals are different; andperforming, by the UE, channel estimation according to the referencesignals.
 2. The channel estimation method according to claim 1, wherein:the reference signals are dedicated reference signals and commonreference signals.
 3. The channel estimation method according to claim1, wherein: the reference signals are common reference signals.
 4. Thechannel estimation method according to claim 3, wherein: the specifictime-frequency lattice is located in a data channel symbol domain of thedownlink signals.
 5. The channel estimation method according to claim 1,wherein: the reference signals are dedicated reference signals.
 6. Thechannel estimation method according to claim 5, wherein: the downlinksignals further comprise common reference signals, and a relativefrequency shift between the common reference signals sent by the firstAP and the second AP is zero.
 7. The channel estimation method accordingto claim 5, wherein: the method further comprises: performing channelestimation by regarding data signals in the downlink signals asinterference signals; estimating the data signals according to a resultof the channel estimation; eliminating the data signals in the downlinksignals according to a result of estimating the data signals; andperforming channel estimation.
 8. The channel estimation methodaccording to claim 5, wherein: no common reference signal is comprisedin any data channel symbol domain except a preset symbol domain in thedownlink signals.
 9. A channel estimation apparatus, comprising: areceiver, configured to receive downlink signals inclusive of referencesignals from a first Access Points (AP) and a second AP, wherein: aspecific time-frequency lattice in the downlink signals sent by thefirst AP does not comprise data signal, the specific time-frequencylattice corresponds to a time-frequency lattice utilized by the secondAP to send a reference signal, and time-frequency lattices utilized bythe first AP and the second AP to send reference signals are different;and an estimating unit, configured to perform channel estimationaccording to the reference signals.
 10. The channel estimation apparatusaccording to claim 9, wherein the reference signals are dedicatedreference signals; the estimating unit further comprises: a firstestimating sub-unit, configured to perform channel estimation byregarding data signals in the downlink signals as interference signals;a second estimating sub-unit, configured to estimate the data signalsaccording to a result of the channel estimation; and a third estimatingsub-unit, configured to eliminate the data signals in the downlinksignals according to a result of estimating the data signals, andperform channel estimation.
 11. The channel estimation apparatusaccording to claim 9, wherein: the receiver is configured to receivedownlink signals from the first AP and the second AP, the downlinksignals include dedicated reference signals and common referencesignals, the specific time-frequency lattice in the downlink signalssent by the first AP does not comprise data signal, the specifictime-frequency lattice corresponds to the time-frequency latticeutilized by the second AP to send the dedicated reference signal; andthe relative frequency shift between the common reference signals sentby the first AP and the second AP is zero.
 12. The channel estimationapparatus according to claim 9, wherein: the receiver is configured toreceive downlink signals inclusive of common reference signals from thefirst AP and the second AP, the specific time-frequency lattice in thedownlink signals sent by the first AP does not comprise data signal, andthe specific time-frequency lattice corresponds to the time-frequencylattice utilized by the second AP to send the common reference signal;wherein the specific time-frequency lattice is located in a data channelsymbol domain of the downlink signals.
 13. The channel estimationapparatus according to claim 10, wherein: the receiver is configured toreceive downlink signals from the first AP and the second AP, thedownlink signals include dedicated reference signals and commonreference signals, the specific time-frequency lattice in the downlinksignals sent by the first AP does not comprise data signal, the specifictime-frequency lattice corresponds to the time-frequency latticeutilized by the second AP to send the dedicated reference signal; andthe relative frequency shift between the common reference signals sentby the first AP and the second AP is zero.
 14. The channel estimationapparatus according to claim 10, wherein: the receiver is configured toreceive downlink signals inclusive of common reference signals from thefirst AP and the second AP, the specific time-frequency lattice in thedownlink signals sent by the first AP does not comprise data signal, andthe specific time-frequency lattice corresponds to the time-frequencylattice utilized by the second AP to send the common reference signal;wherein the specific time-frequency lattice is located in a data channelsymbol domain of the downlink signals.
 15. A channel estimation system,comprising: a first Access Points (AP) and a second AP, wherein: thefirst AP and the second AP are configured to send downlink signalsinclusive of reference signals to a User Equipment (UE), a specifictime-frequency lattice in the downlink signals sent by the first AP doesnot comprise data signal, the specific time-frequency latticecorresponds to a time-frequency lattice utilized by the second AP tosend a reference signal, and time-frequency lattices utilized by thefirst AP and the second AP to send reference signals are different. 16.The system according to claim 15, wherein the first AP and the second APare configured to send downlink signals inclusive of dedicated referencesignals and common reference signals, the specific time-frequencylattice in the downlink signals sent by the first AP does not comprisedata signal, the specific time-frequency lattice corresponds to thetime-frequency lattice utilized by the second AP to send the dedicatedreference signal; and the relative frequency shift between the commonreference signals sent by the first AP and the second AP is zero. 17.The system according to claim 15, wherein the first AP and the second APare configured to send downlink signals inclusive of common referencesignals, the specific time-frequency lattice in the downlink signalssent by the first AP does not comprise data signal, and the specifictime-frequency lattice corresponds to the time-frequency latticeutilized by the second AP to send the common reference signal; whereinthe specific time-frequency lattice is located in a data channel symboldomain of the downlink signals.